Concepts for the use of high energy particle beams for military applications have been in existence for more than two decades. During this period, extensive theoretical and experimental effort have been performed, and many workers have contributed to the development and evaluation of these efforts. Both ground based and space based systems have been studied and both are currently under development for some applications.
One space based system that is currently being developed utilizes neutral particle beams. Contrasted to charged particle beams, neutral particle beams have several inherent properties that make them very attractive for space based applications. In particular, high energy neutral particles propagate in straight lines unaffected by the earth's magnetic field and have a very brief flight time to targets even at extended ranges. In addition, the neutral particles become high energy charged particles upon interaction with the surface of a target and penetrate deeply into the vehicle, thus making shielding relatively ineffective. In the case of a nuclear warhead, these particles are capable of heating the nuclear material by fission processes, neutron generation and ionization. For non-nuclear material, heating is produced by ionization, possibly producing kill by thermal initation of the weapon's high explosive. Thus, interest in space based systems was revitalized when experiments, at the Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF), on the proton linear accelerator showed several orders of magnitude improvement in accelerator performance. Extensive measurements of beam properties at energies of 211 and 500 MeV showed that the energy spread of the beam was better than 0.5% and the emittance of the beam was better than 0.66.pi.cm-mrad. In addition, the LAMPF accelerator has been used to accelerate H.sup.- ions to energies above 100 MeV and, as expected, their behavior is similar to that of protons. These achievements prompted Knapp and NcNally to write a LASL report titled SIPAPU Rpt. LA-5642-MS, Los Alamos Scientific Laboratory, July 1974, in which they proposed a satellite-based high energy neutral hydrogen weapon. Their device is depicted schematically in FIG. 1. An intense, high quality beam of H.sup.- ions is generated and accelerated to an energy of approximately 250 MeV. After acceleration the beam is expanded, and passed through final focusing and steering magnets. The beam is subsequently neutralized by stripping the weakly bound electron from the H.sup.- ion and the resulting hydrogen beam propagates toward the target unaffected by the earth's magnetic fields. Both the system and the target must remain above approximately 250 kilometers in order to minimize the beam degradation by collisions with residual gases.
Improvements in the state of the art for producing intense high quality ion beams, for lightweight efficient accelerators, for high current negative ion beams stripper techniques without excessive scattering, and for compact lightweight power systems are necessary before this device can be considered viable. Methods for neutral beam detection, signatures for closed loop tracking and kill assessment, and techniques for rapidly steering the beam over large angles are also needed.
Although, there are many of these practicle issues to be considered, there does not appear, in principle, to be any inherent limitations that deem the device inviable. And, many of these practicle issues have been or are being overcome. But the current solutions for the neutralization of the H.sup.- ion beams all have serious adverse systems implications.
Once the H.sup.- beam has been accelerated, aimed, and focused on the target it can be neutralized. This can be accomplished by a number of techniques. For example, photo detachment, a plasma or gas stripping have been considered. Photo detachment causes less degradation in beam quality and can result in the largest friction of the ion beam being converted to a neutral beam. Unfortunately, extremely high energy cw lasers at wavelengths that are not currently available are required for this purpose, and, even if they become available, they would probably be as large and as expensive as the rest of the system. Since open-ended plasma strippers with quiescent plasmas cause less beam degradation than a gas stripper they have also been considered; but, because of the necessity of allowing the plasma to escape, the power requirement for the plasma stripper alone in equal to or greater than that for the rest of the system. Also, it is problematical that a sufficiently quiescent plasma could be produced. Therefore, considerable work both theoretical and experimental has been devoted to the development of a gas stripper. The important results of this work is summarized in FIG. 2 where the fractions of the initial beam which survives as H.sup.-, which is stripped to H.sup.o, and which is stripped to H.sup.+ is given as a function of the stripper thickness.
As a result of this work a gas stripper is now included in the SIPAPU system. However, this is also an open system where the gas escapes out the ends. Part of this gas expands back into the H.sup.- beam optical system where stripping collisions occur before the beam has been made parallel and these particles are therefore not directed toward the target. The rest of this gas escapes out in the forward direction where additional stripping collisions occur producing H.sup.+ particles which do not reach the target because of the effect of the earth's magnetic field. As can be seen, there is a need for a better and more efficient way to strip H.sup.- ion beams to H.sup.o ion beams.
Therefore, it is an object of this invention to provide a neutralization device that overcomes many adverse effects on the system in which this device is to be used.
Another object of this invention is to replace the low pressure gas stripper with a solid stripper that is made of very thin material.
A still further object of this invention is to replace the low pressure gas stripper with a solid stripper that is made of a material such as saran wrap, mica, cellophane, or the like.
Other objects and advantages of this invention will be obvious to those skilled in this art.